This invention relates to a method and apparatus for measuring a lighting condition of an object having one or more colors.
Colors reflected from objects (e.g., printed materials, images displayed on a computer monitor, etc.) are perceived differently by human observers under varying lighting conditions. For example, a blue sheet of paper may appear to emit a greenish tinge in a room having a fluorescent light source while the same blue sheet of paper may appear to emit a yellowish tinge in another room equipped with incandescent lighting.
Conventional color management systems, such as systems based upon the ICC Profile Format, are widely used in the graphic arts and image processing fields. These conventional systems usually control tristimulus values to effect equivalent color reproduction. For example, to reproduce a printed image with colors equivalent to the original under different lighting conditions, a chromatic adaptation transform is applied to compensate for white point differences, and a color signal transform is applied to transform the tristimulus values into the specific color signals for an output device. However, this conventional method is deficient and often fails to yield accurate results, largely due to the fact that spectral information is ignored.
Accordingly, to predict an object""s true color where lighting conditions in a particular room alter the object""s color, the object""s light reflective properties must be reconciled with the lighting conditions. In particular, to predict the true color of an object having spectrally non-selective reflectance factors, information is needed regarding the lighting conditions in the object""s particular location. In this case, tristimulus values of light reflected from the object can be calculated from the illuminance and chromaticity coordinates of light irradiated onto the object using conventional mathematical normalization techniques. Similarly, to predict the true color of an object having spectrally selective reflectance factors, information is needed regarding the lighting conditions in the object""s particular location (i.e., spectral irradiance). Tristimulus values of light reflected from an object can be calculated from linear combinations of color matching functions, the object""s spectral reflectance factor, and the spectral irradiance.
Predicting the actual colors of objects is desirable for a number of reasons. For example, an image processing device in different lighting conditions could use such information to process images to compensate for any potential color distortions caused by the lighting conditions. By modifying the images in this manner, images could be displayed on a computer display device emitting their actual colors, as if undisturbed by spectral irradiance. Another example includes using such information to alter data representing materials to be printed out to account for possible effects of spectral irradiance upon the printed material.
Unfortunately, heretofore highly specialized and expensive instruments have been necessary for measuring lighting conditions, including spectral irradiance and illuminance and chromaticity coordinates, within an acceptable degree of accuracy. The expense of these instruments has made them prohibitive for many applications. Additionally, a high degree of technical prowess, advanced mathematical skills and/or training are required to operate such conventional lighting condition measurement equipment.
Accordingly, a need exists for a method and apparatus that could be used for measuring lighting conditions without requiring the utilization of any highly specialized, expensive instruments or requiring a great deal of technical prowess, advanced mathematical skills and/or training. Moreover, it would be advantageous if such a method and apparatus could be easily installed, configured, used and maintained.
A method for measuring a lighting condition of an object having one or more colors in accordance with one embodiment of the present invention includes a few steps. In this method, one or more samples are provided with each of the samples having one or more colors. One of the colors of the object is compared against one of the colors of one of the samples. The color of the sample being compared is defined by a plurality of color attribute values. At least one of the plurality of color attribute values representing the color of the sample being compared is adjusted until the color of the sample appears to substantially match the color of the object. Once the color attribute values are adjusted, the lighting condition of the object is determined based on the adjusted plurality of color attribute values.
An apparatus for measuring a lighting condition of an object having one or more colors in accordance with another embodiment of the present invention includes a display device, a color attribute interface, and a processing system. The display device displays one or more samples for comparing one of the colors of the object against one of one or more colors of one the samples. The color attribute interface is used to adjust at least one of a plurality of color attribute values representing the color of the sample until the color of the sample appears to substantially match the color of the object. The processing system determines the lighting condition of the object based on the adjusted plurality of color attribute values.
A program storage device readable by a machine tangibly embodying a program of instructions executable by the machine to perform a method for determining a lighting condition of an object having one or more colors includes providing one or more samples, each of the samples having one or more colors; comparing one of the colors of the object against one of the colors of one of the samples, the color of the sample being compared defined by a plurality of color attribute; adjusting at least one of the plurality of color attribute values representing the color of the sample being compared until the color of the sample appears to substantially match the color of the object; and determining the lighting condition of the object based on the adjusted plurality of color attribute values.
One of the advantages of the present invention is that the lighting condition in a room may be measured without requiring the utilization of any highly specialized, expensive instruments or requiring a great deal of technical prowess, advanced mathematical skills and/or training. Moreover, the lighting condition measurements taken in accordance with the present invention are accurate to an acceptable degree and do not require a great deal of effort or time on the part of the user. Further, the present invention is easily installed, configured, used and maintained.